Additional to the Fungi: FUNGI IMPERFECTI. Incompletely known (_Saccharomyces_, _Oidium_-forms, etc.). Class 1. =Phycomycetes (Algal-Fungi).=[12] This group resembles _Vaucheria_ and the other Siphoneæ among the Algæ. ORGANS OF NUTRITION. The mycelium is formed of a single cell, often thread-like and abundantly branched (Fig. 78). Vegetative propagation by chlamydospores and oidia. Asexual reproduction by endospores (sometimes _swarmspores_) and conidia. Sexual reproduction by conjugation of two hyphæ as in the Conjugatæ, or by fertilisation of an egg-cell in an oogonium. On this account the class of the Phycomycetes is divided into two sub-classes: ZYGOMYCETES and OOMYCETES. Sub-Class I. =Zygomycetes.= Sexual reproduction takes place by zygospores, which function as resting-spores, and arise in consequence of _conjugation_ (Fig. 81); in the majority of species these are rarely found, and only under special conditions. The most common method of reproduction is by endospores, by acrogenous conidia, by chlamydospores, or by oidia. _Swarmspores are wanting._ Parasites and saprophytes (order 6 and 7). The zygospores are generally produced when the formation of sporangia has ceased; _e.g._ by the suppression of the sporangial-hyphæ (_Mucor mucedo_), or by the diminution of oxygen; _Pilobolus crystallinus_ forms zygospores, when the sporangia are infected with saprophytic _Piptocephalis_ or _Pleotrachelus_. =A.= Asexual reproduction only by sporangia. Order 1. =Mucoraceæ.= The spherical sporangia contain many spores. The zygospore is formed between two unicellular branches (gametes). The unicellular mycelium (Fig. 78) of the Mucoraceæ branches abundantly, and lives, generally, as a saprophyte on all sorts of dead organic remains. Some of these Fungi are known to be capable of producing _alcoholic fermentation_, in common with the Saccharomyces. This applies especially to _Chlamydomucor racemosus_ (_Mucor racemosus_), when grown in a saccharine solution, and deprived of oxygen; the mycelium, under such conditions, becomes divided by transverse walls into a large number of small cells. Many of these swell out into spherical or club-shaped cells, and when detached from one another become chlamydospores, which abstrict new cells of similar nature (Fig. 79). These chlamydospores were formerly erroneously termed “mucor-yeast,” but they must not be confounded with the yeast-conidia (page 94). They are shortened hyphæ, and are not conidia of definite size, shape, and point of budding. Oidia are also found in _Chlamydomucor_. [Illustration: FIG. 78.--_Mucor mucedo._ A mycelium which has sprung from one spore, whose position is marked by the *: _a_, _b_, _c_ are three sporangia in different stages of development; _a_ is the youngest one, as yet only a short, thick, erect branch; _b_ is commencing to form a sporangium which is larger in _c_, but not yet separated from its stalk.]